airbag vs hot-air balloon

airbag

noun
  • A similar inflated bag used in performing stunts, etc. 

  • A person who talks too much; a windbag or gossip. 

  • A protective system in automobiles in which when a crash occurs, a bag containing nitrogen, formed by the explosive decomposition of sodium azide, quickly inflates in front of the driver or passenger, preventing injury to the head. Side air bags, including the back seat passengers, also prevent injury. 

hot-air balloon

noun
  • A balloon-shaped aircraft whose bag is inflated with hot air; it carries passengers and crew in a gondola slung underneath. 

How often have the words airbag and hot-air balloon occurred in a corpus of books? (source: Google Ngram Viewer )